The present invention relates to a rotating flexible shaft having tips or ends adapted to engage mating elements of driving or driven members; and more particularly to a flexible shaft having a wire wound outer layer.
Rotary shafts for transmitting torque typically have square ends adapted to engage square recesses of mating driving and driven parts. Rotary flexible shafts commonly used to transmit torque from a motor to adjust a seat in a motor vehicle, for example, are disposed within cylindrical casings which eliminate buckling and isolate the rotating shaft from contact with adjacent structures.
For “perceived quality” reasons, especially in consumer products, it is desirable to reduce noise due to rattle between the rotating shaft and the surrounding casing and/or the driving and driven components to the greatest extent practicable. For this purpose it is known to replace one of the wires in the outer wire wound layer of the flexible shaft with a cord, strand or thread of relatively soft material (compared to that of the casing) such as flocked yarn. The terms cord, strand and thread are used interchangeably herein.
Eichenberger et al. European Patent EP 1286065 discloses such a shaft, in which a wire of the outer layer is omitted to leave a gap, and flocked yarn having a diameter greater than that of the outer layer wires is wound into the gap; so that the yarn contacts the inner wall of the casing and isolates the wires from the wall, thus reducing noise when the shaft is rotated.
However, omission of an outer layer wire in Eichenberger et al. reduces the consistency of pitch of the outer layer and allows the gap in which the yarn is disposed to vary in width as the shaft is manufactured and processed, thus diminishing the consistency of the protrusion of the flocked yarn. Omitting a wire also reduces the useful life of the shaft.
In U.S. Pat. No. 3,389,579 to Werner et al. entitled Shaft Guided In A Protection Tube, noise isolation between a flexible shaft and a surrounding protection tube is provided by adhering short elastic fibers to the outer surface of the shaft or the inner surface of the protection tube, to form a brush-like layer between the shaft and tube.
In U.S. Pat. No. 4,411,168 to Yoshifuji entitled Inner Cable, noise due to contact between a push-pull wire wound flexible cable and a surrounding conduit is reduced by winding a hollow elastic member on the cable core between wire teeth also wound on the core, the elastic member having a greater diameter than the teeth so that only the elastic member contacts the inner surface of the conduit, thus reducing noise when the cable is moved longitudinally.
In U.S. Pat. No. 4,849,038 to Burghardt entitled Method For Depositing An Interlining On A Pitched Cable For Reducing Friction And Noise, a filament flocked with abrasion resistant material is wound or deposited on a wire wound flexible shaft, interleaved with the wire of the outer layer of the shaft.
In U.S. Pat. No. 7,717,795 to Mellor, a deformable polytetrafluoroethylene sheath is applied over the ends of a flexible shaft to reduce noise and vibration due to friction and relative movement between the shaft ends and mating recesses.
Accordingly, an object of the present invention is to provide a rotary flexible shaft that exhibits low rotational noise when coupled between driving and driven members and disposed within a surrounding casing.